The present invention relates to the production of disilane from monosilane by means of plasma discharge.
A plasma represents a partially or entirely ionized gas, in which positive, negative and neutral molecules exist in close proximity to each other in an overall neutral environment.
The fact that electric discharges, with which non-equilibrium plasmas are produced, are suitable for the production of higher silanes starting from monosilane was first demonstrated by E. J. Spanier and A. G. MacDiarmid (Inorg. Chem. 1 (1962) 432/3. The ozonizer (ozone producer) used by Spanier et al. supplies a 63% yield of a mixture of 66% Si.sub.2 H.sub.6, 23% Si.sub.3 H.sub.8 and 11% higher silanes, while the remaining 37% is deposited in the form of an amorphous layer on the inside walls of the ozonizer.
Production of disilane from monosilane with the help of the silent electric discharge at atmospheric pressure and/or higher pressure is disclosed in Japanese patent specification 60/127 214 (C. A. 1986, 104:7722 m).
RF-discharges (high frequency luminous discharges) are indicated by Dickson (U.S. Pat. No. 4,568,437) for the production of disilane with a yield of approximately 40%, based on the reacted monosilane. A pressure of 1 to 2 torr and a temperature of 120.degree. to 300.degree. C. are used in this process.
However, here too the formation of an undesirable amorphous silicon layer on the walls of the reaction vessel cannot be avoided, which therefore requires further research.
European patent application 0 143 701 relates to the deposition of amorphous silicon layers by thermal decomposition of disilane. According to the process described in this specification, this compound is obtained by reaction of monosilane with atomic hydrogen, which is produced outside the reaction zone by microwave discharge in a hydrogen atmosphere.
Precise parameters of the process such as for instance the amount of charge fed in and the hydrogen concentration and/or a disilane yield however are not disclosed.